1. Field of the Invention
The present invention generally relates to ink jet printer technology and, more precisely, to a method and apparatus for priming a thermal ink jet pen.
2. Description of the Related Art
In general, thermal ink jet technology involves using thermal excitation to boil ink and ejecting droplets of ink through tiny orifices in an ink jet pen printhead nozzle plate in order to form patterns of dots on paper. A general description of ink jet technology can be found, for example, in the Hewlett Packard Journal, Volume 36, Number 5, May 1985, incorporated herein by reference.
One of the inherent difficulties of ink jet printing is the necessity to ready a pen for operation. For example, when attaching a new pen to a printer or after a period of non-usage, ink may not be present at the orifices.
FIG. 2 depicts a typical disposable pen cartridge 2, having an integral ink storage reservoir compartment 4, and a printhead 6, having a nozzle plate 8. In order to have acceptable printing occur on first demand, it is desirable to prime the printhead, i.e. to fill an ink holding chamber generally located between the plate 8 and a thin-film substrate which includes a resistor/heater structure of the printhead 6. A disposable ink jet head is described in U.S. Pat. No. 4,500,895 (Buck et al.), assigned to the common assignee herein.
Several systems have been developed to accomplish ink jet priming. MIRANDA ET AL., U.S. Pat. No. 4,517,577, use a pressurized ink supply and flow ink through a manifold which is adjacent to scoop lines leading to reservoirs which are subjacent each orifice. A valve mechanism allows ink to flow through the manifold to the scoops during a priming cycle.
GEIL, U.S. Pat. No. 4,170,016, shows a manual, plunger pump for pressurizing a remote ink source, using a relief valve to ensure that the pen is not over-pressurized during priming.
HERRNRING, U.S. Pat. No. 4,573,819, shows a permanently collapsible primary reservoir using an electrical motor to pump ink from the primary reservoir to a secondary reservoir requiring a charging valve connection between the two reservoirs.
Such prior systems are complicated and cumbersome and, more particularly, are not amenable to more modern systems where, for example, the pen and self-contained ink reservoir(s) may be of a disposable type as shown in FIG. 2.